1. Field of the Invention
The present invention relates to an improvement in a substrate holder for liquid phase epitaxial growth for use in manufacturing semiconductor devices.
Particularly, the present invention concerns an improvement in a substrate holder for holding semiconductor substrate in a liquid phase epitaxial growth process in manufacturing semiconductor devices.
2. Prior Art
Liquid phase epitaxial growth method utilizing gallium as solvent is widely used in forming epitaxial layers such as GaAs, Gap or GaAlAs on a semiconductor substrate. The liquid phase epitaxial growth method is indispensable in manufacturing semiconductor lasers or light emitting diodes.
In such liquid phase epitaxial growth method, semiconductor substrate is covered by a solution containing suitable semiconductor and gallium as solvent. FIG. 1 shows schematic sectional view of a conventional apparatus for liquid phase epitaxial growth having a conventional substrate holder, wherein a substrate holding arm 2 and a substrate holding screw 3 fixed thereto are provided in a container 1, all of them being made of quartz. A semiconductor substrate 4 is held by the screw 3 on the holding arm 2 in the upper part of the container 1, and a semiconductor solution 5 is filled in the lower half part of the container 1. Then, after heating the container 1 at a predetermined temperature, it is turned upside down as shown by an arrow A. Then, the semiconductor substrate 4 is immersed in the solution 5, thereby an epitaxial growth on the substrate 4 is made.
FIG. 2 is a schematic sectional side view of essential part of another example of the conventional way of the epitaxial growth wherein a container 6 of a semiconductor solution 5 is made as a separate body from a substrate holder comprising a substrate holding arm 2 and a holding screw 3. In this second conventional example, a substrate 4 is put into the solution 5 by simply moving down the holding arm 2, and the epitaxial growth is made.
FIG. 3 is an enlarged sectional side view of the substrate holder part, i.e., the screw 3 holding the semiconductor substrate 4 on the holding arm 2. When such holding part is immersed in the solution for the epitaxial growth, due to difference of boundary conditions of the holding part from those of other parts of the substrate, condition of epitaxial growth of the substrate holder part becomes different from those of the abovementioned other parts. Therefore, thickness of the epitaxial layer near the substrate holder part becomes different from those of other parts, or an irregular growth layer 7 is formed near the substrate holder part as shown in FIG. 4 and it necessitates additional steps of removing it in the manufacturing process.